This invention relates to an optical transmission system as set forth in the preamble of claim 1.
WO 95/05041 discloses a system for optically transmitting information from a subcenter to a plurality of optical network units via a plurality of optical transmission lines. The subcenter is connected to the optical network units by a passive optical distribution network consisting of optical transmission lines and an optical splitter. At the subcenter, a plurality of electric subcarrier signals are combined into a frequency-division multiplex signal and subsequently converted from electrical to optical form. The subcarrier signals are television signals, for example, which are destined for all optical network units, and telephone signals, each of which is destined for only one of the optical network units. For the telephone signals, unlike the television signals, only a small frequency range is reserved. If a multitude of customer locations are connected via the optical network units to the subcenter, this relatively small frequency range does not suffice to make available a sufficient number of channels for the multitude of customer locations.
It is therefore an object of the invention to provide an optical transmission system which can transmit different information to a plurality of optical network units more flexibly.
This object is attained by the teaching of claim 1. The invention is characterized in that the system comprises a plurality of nodes for optically transmitting further information and a plurality of optical couplers, and that the further information of each of the nodes is fed via a respective coupler into a transmission line connected to only part of the plurality of optical network units. The combination of the information, for example television signals, and the further information, for example telephone signals, via the optical couplers and the division of the further information among those transmission lines which are connected to the respective optical network unit for which the respective further information is exclusively intended optimize the utilization of the available transmission capacity. Furthermore, the expansion capability of the system is improved, since for each further optical network unit, for example, only one additional optical transmission and one optical splitter are needed.